Process of reducing iron oxide ores with gases containing carbon monoxide



United States Patent Ofilice 3,377,156 Patented Apr. 9, 1 968 3,377,156PROCESS OF REDUCING IRON OXIDE ORES WITH GASES CONTAINING CAR- BONMONOXIDE Theodore Kalina, Elizabeth, and John A. Kivlen, Sparta,

N.J., assignors to Esso Research and Engineering Company, a corporationof Delaware N Drawing. Filed July 30, 1965, Ser. No. 476,159 15 Claims.(Cl. 7526) ABSTRACT OF THE DISCLOSURE The reversion of gases containingcarbon monoxide to carbon dioxide and carbon when in contact withcatalytic metal surfaces at high temperatures is suppressed or inhibitedby providing small concentrations of sulfur or heat-decomposable sulfurcompounds in the gases. This invention is especially useful in directiron ore reduction processes.

This invention relates to the production of metallic iron via reductionof iron ores by contact with reducing gases. In particular, it relatesto an improved iron ore reduction process wherein fluidized iron oresare metallized by direct contact with carbon monoxide, mixtures ofcarbon monoxide and hydrogen, or mixtures Ofcarbon monoxide with othergases which can also contain hydrogen.

It is well known to produce metallic iron by reduction of oxidic ironores, i.e., ores containing or consisting essentially of oxides of iron,in beds fluidized by ascending gases, at temperatures ranging generallyfrom about 1000 F. up to just below the sintering temperature, i.e.,about 1800 F. for most ores. In such processes, several fluidized bedsare generally provided, and these are staged as separate reduction zonesoperated at the same or different elevated temperatures. Generally, theseveral fluidized beds are housed within a single reactor.

In a typical staged fluidized iron ore reduction process, particulateoxidic iron ores are introduced into the top of a reactor and floweddownwardly from one fluidized bed to the next succeeding bed, and withineach bed the state of oxidation of the ore is progressively lowered.Thus, the ore flows from one of a series of staged reduction zones tothe next lower succeeding stage. Within each of the several stages, theore is contacted by upwardly flowing gases, and reduced whileconcurrently the reducing components of the ascending gas is oxidized.If desired, the partially oxidized gas can be regenerated by removal ofoxidized components and reused. In the several stages, the ore isreduced, e.g., from ferric oxide to magnetic oxide of iron (or mixtureapproximating the composition of such compound), from magnetic oxide ofiron to ferrous oxide, and from ferrous oxide to substantially metalliciron. Generally, the metallic iron product ranges from about 85 to about95 percent, and higher, metallic iron.

Such fluidized iron ore reduction processes most often utilizeexternally generated synthesis gas, i.e., gaseous mixtures consisting ofcarbon monoxide and hydrogen, or mixtures of these and other gases,which are injected into the bottom stage of the reactor. Such gaseousmixtures are generally formed from hydrocarbon fuels which are oxidizedor burned in a deficiency of oxygen. Often such gaseous mixtures arehydrogen-enriched, e.g., via use of the water-gas shift reformingreaction. Because of the endothermic nature of hydrogen in the iron orereduction reaction, however, it is generally desirable to employ gaseousmixtures wherein carbon monoxide is employed in relatively highconcentration in the process.

Often also, it is desirable to form the reducing gas mixtures, in wholeor in part, in situ. In accordance with this technique, generally termeddirect injection, hydrocarbon fuels are fed directly into a stage of theprocess wherein metallization is high, e.g., perhaps to about 98percent, so that the reducing gases are generated internally. Thus,metallic iron is catalytic under certain conditions and the fuel isdecomposed in situ to a gaseous mixture of carbon monoxide and hydrogen.The presence of carbon monoxide in the gaseous mixture, whetherintroduced into or generated in situ within the process, is quitedesirable, but its presence often creates difiiculties.

Gases which contain carbon monoxide even in relatively lowconcentrations will, under certain conditions, strongly react in thepresence of certain metals, particularly iron. Certain forms ofliberated carbon will vigorously and rapidly combine with the iron,e.g., the reactor and auxiliary equipment made of iron, so that a severeform of corrosion, i.e., catastrophic carburization, often results.Moreover, free carbon will be formed. This lessens efliciency.Further-more, the deposition of carbon, inter alia, by reversion of thecarbon monoxide to free carbon, causes plugging and failure of e.g.standard heating equipment, pumps and transfer lines. These problems aremost acute when carbon monoxide and mixtures of gases containing carbonmonoxide are heated at temperatures ranging from about 800 F. to about1300 F. In fluidized iron ore reduction processes, it is extremelydiflicult, if indeed possible, to avoid heating such gases through thistemperature range and hence the reversion of carbon monoxide to carbon,or creation of conditions for catastrophic carburization is an acutethreat.

Even in processes wherein carbon monoxide-containing gaseous mixturesare desirably heated to higher temperatures, e.g., temperatures rangingfrom about 1300 to about 1800? F., it is extremely diflicult, ifpossible, to avoid cooling the gas through such temperature range. Thus,it is often desired to regenerate the reducing gases for further use byremoval of carbon dioxide and water. But, to do so the gases rnust becooled through this temperature range. On the other hand, it is oftendesired to elevate the temperature of a cool gas through this range.Thus, gas preheating is one method of introducing heat to the process.The carbon monoxide reversion problem, then, has been extremelytroublesome and has handicapped the development of both indirect anddirect injection techniques for the generation and use of carbonmonoxide-containing gaseous mixtures in fluidized iron ore reductionprocesses.

The solution of these and other difliculties is therefore the primaryobjective of the present invention. In particular, it is the object ofthis invention to provide a new and improved process which will makefeasible the more general use of carbon monoxide-containing reducing gasmixtures by obviating the problems due to carbon monoxide reversion.More particularly, the objective of this invention is to provide aprocess which will suppress or inhibit reversion of carbon monoxide. Afurther and more specific objective is to provide the art with asimplified, new and novel fluidized iron ore reduction process,especially one utilizing a series of staged reduction zones, whereincarbon monoxide reversion is drastically suppressed even at temperatureswhich normally produce acute carbon reversion. It is yet another objectto provide such process which is particularly useful in directhydrocarbon injection.

These and other objects are achieved in accordance with the presentinvention which contemplates the use of small and infinitesimalquantities of sulfur or heat decomposable sulfur-containing compoundsinjected, added to, admixed with or otherwise'incorporated within thecarbon monoxide-containing reducing gas in contact with catalyticmetallic surfaces, especially ferrous metal surfaces, e.g., iron. Suchprocess finds particular application in a fluidized iron ore reductionprocess. By use of such compounds within the carbon monoxide gas, orgaseous mixture containing carbon monoxide, the gas can be utilized inreducing the iron ore and the reversion of carbon monoxide will besuppressed; and, in some instances virtually eliminated. In particular,it has been found that such gases can be heated or cooled throughtemperatures ranging from about 800 F. to about 1500" F., andparticularly, even from about 900 F. to about 1200 F., even in thepresence of metals, but yet carbon monoxide reversion is drasticallyinhibited or suppressed.

It has been found that as little as one part of sulfur, per millionparts of gas can be of some beneficial effect in lessening carbonmonoxide reversion in the gaseous reduction mixture. Preferably,however, it is desirable to employ at least about parts to about 1000parts, and more preferably from about to about 300 parts of sulfur, permillion parts of gas, since this concentration effectively suppressescarbon monoxide reversion, and yet does not create significant problemsdue to acid formation. Under most conditions, optimum benefits areproduced by employing from about to about 200 parts sulphur, per millionparts of gas. While sulfur concentrations greater than about 1000 partsper million parts of carbon monoxide can be employed, this is notgenerally desirable inasmuch as, inter alia, acid formation increasesand there is little, if any, corresponding benefit resulting from theuse of the increased sulfur concentration. Significantly higher amountsof sulfur can adversely affect the quality of the resultant metallizedproduct.

The reason for the effectiveness of sulfur or heatdecomposablesulfur-containing compounds in suppressing carbon monoxide reversion isnot known. It is believed, however, that the sulfur or sulfur compoundsdecompose in the process to provide an effective concentration ofhydrogen sulfide in situ and hence, it is believed that it is in thehydrogen sulfide which actively suppresses carbon monoxide reversion. Itis certainly known, however, that hydrogen sulfide is extremelyeffective, whether added abinitio or generated in situ, and willsuppress carbon monoxide reversion when present in very smallconcentrations. Therefore, sulfur or any sulfur-bearing compound whichwill decompose at temperatures below about 1500 F. to form an effectiveconcentration of hydrogen sulfide can be directly employed. On the otherhand, sulfur-bearing compounds decomposable at higher temperatures canbe indirectly heated to higher temperatures outside the process, or at aspecific location within the process, and then injected into the processto suppress carbon monoxide reversion.

Additives particularly suitable for use in accordance with the presentinvention, whether added to the process ab initio or generated in situ,are the divalent sulfur compounds, or sulfides. These can becharacterized by the following formula wherein R and R are the same ordifferent and can be hydrogen or monovalent organic radicals, e.g.,hydrocarbon radicals, such as alkyl, alkenyl, alkynyl, aryl, arylalkyl,aralkyl and the like. The organo radicals can be substituted orunsubstituted, and where substituted the hydrogen of the radical may bereplaced by halogen, nitro groups, amino groups, carbonyl groups and thelike; or, the radical, where of ring structure, can be ring substitutedto form a heterocyclic radical. The carbon of a ring can be substituted,for example, by sulfur, oxygen, nitrogen, or the like. Preferably, anorgano radical should contain no more than about ten carbon atoms, andmore preferably about six carbon atoms. Exemplary ofthese classes ofcompounds are methyl sulfide, n-propyl sulfide, ethyl n-propyl sulfide,cetyl isoamyl sulfide, bis(trichloromethyl) sulfide, allyl benzylsulfide, phenyl trichloromethyl sul- 4 fide, l-naphthyl phenyl sulfide,anthrene, 3(ethylmercapto) thiophene, anethiol, 8-quinolinethiol and thelike.

Preferably, the sulfides contain no more than one monovalent organoradical. Exemplary of such compounds are methyl mercaptan, isopropylmercaptan, n-amyl mercaptan, allyl mercaptan, 3-acridinemercaptan,a-methyl benzyl mercaptan, Z-naphthalene thiol and the like. Mixtures ofany of such compounds with other substances or with each other aresuitable. Certain commercial mixtures and naturally occurring materialscan also provide these compounds, or can be added to the process, togenerate the desired compounds in situ.

Most preferably R and R are both hydrogen, i.e., hydrogen sulfide.Hydrogen sulfide is an outstanding compound because of its availability,its readily usable form, and its extremely high effectiveness in minuteconcentrations.

More complex sulfur compounds can also be employed. Other divalentsulfur compounds are thus suitable. These include such compounds as thepolysulfides, especially the disulfides illustrative of which are carbondisulfide, methylethyl disulfide, Z-fenchanyl methyl disulfide,tertbutyl-Z-naphthyl disulfide, 2-(o-nitrophenyldithio)benzothiazole,and the like.

In a particularly preferred embodiment according to this invention,oxidic ores, as particulate solids particles, are contacted andfluidized with upwardly flowing carbon monoxide-containing gases in aprocess wherein a plurality of staged zones are provided. The zoneswhich contain the fluidized beds of ore at different stages of reductioncan be operated at the same or at different elevated temperatures.Preferably, also, there is provided in accordance with such embodiment,one or more ferric reduction zones operated at temperatures ranging fromabout 1000 F. to about 1800" F. and one or more, and preferably aplurality, of ferrous reduction zones operated at temperatures rangingfrom about 1300 F. to about 1700 F. The sulfur or sulfur-containingcompound, or compounds, is preferably added to the carbonmonoxide-containing reducing gas and then heated prior to or at the timeof the injection into the process. Preferably, the carbonmonoxide-containing reducing gases within which is provided the sulfuror sulfur-containing compound is injected into a ferrous reduction zonewherein the metallization ranges from about 85 percent to about 98percent, and higher.

The following nonlimiting examples and pertinent dem- .onstrations bringout the more salient features and provide a better understanding of theinvention.

A large quantity of raw hematite ore, i.e. a Carol Lake ore, ispulverized in a ball mill, to a particle size ranging from about to 210microns, and divided into several like portions.

9-methyl mercaptophen- 3-ethylcyclohex- Example 1 A portion of the .oreis charged into a fluidized iron ore reactor or reductionprocess whereinis provided a series of four staged fluidized zones, two ferricreduction zones and two ferrous reduction zones. The ore is fluidized byan upwardly flowing gas initially of 20 percent carbon monoxide, 60percent hydrogen, and 20 percent nitrogen to which is added parts ofhydrogen sulfide, per million parts of gas. The gas is preheated througha temperature range of 850 F. to 1300 F. and then injected into thelowermost ferrous reduction zone from whence it flows from a zonecontaining an iron ore at a lower level of oxidation to the next higherlevel of oxidation, i.e., from the bottom to the top of the reactor. Inthe top ferric zone the partially oxidized gas is burned with air toprovide heat to the various reduction stages and the reduced ore movesfrom the top to the bottom of the reactor from one stage of reduction tothe next. The ferric reduction stages, wherein ferric oxides are reducedessentially to magnetic oxides of iron, are operated at 1300 F. as werethe'ferrous reduction stages wherein the ferrous 5 oxide is reduced, inthe final stage, to provide 94 percent metallization.

Pursuant to operating at such conditions, the process does not show anysignificant sign of carbon monoxide reversion even after many hours ofcontinuous operation. There is no indication whatsover of catastrophiccarburetization.

Example 2 The foregoing demonstration is repeated in precise detai'lemploying a second portion of the ore except in this instance 150 partsof hydrogen sulfide, based on the volume of the gas, is added to theentering gas charged into the ferrous reduction zone. The beds appearnormal and the process functions normally in every way and there is noevidence of any significant amount of carbon monoxide reversion. Theferrous metal parts of the equipment are not carburized and littlecarbon is formed in the reaction.

Example 3 When Example 2 is repeated with another portion of ore heatedto a temperature of 1400 -F. and ethyl mercaptan in concentrations of200 parts, per million parts of carbon monoxide, is added to thereducing gas mixture, there is yet no significant evidence of carbonmonoxide reversion.

Example 4 When the conditions of operation of the process of Example 2are repeated except that 200 parts of benzyl mercaptan is injected intothe process, there is little evidence of carbon monoxide reversion.

When ethyl sulfide, phenyl sulfide, and ethyl propyl sulfide,respectively, are successively added to the process in 100, 150, and 200parts significant benefits also result. The tendency of carbon monoxideto revert is effectively suppressed.

-It has been concluded and firmly established that the sulfur compoundsof this invention must be gasified and thoroughly dispersed Within thereducing gases at the time of reduction to provide benefits, Whetheradded ab initio or generated in situ from an added material capable ofproducing such compounds.

It is apparent that certain modifications and changes can be made in thepresent process without departing the spirit and scope of the invention.The key and novel feature of the invention is the use of small and minorportions of sulfur or heat-decomposable sulfur compounds directly addedto, injected within, or otherwise physically dispersed with the reducinggases at the time of use or injection into the fluidized iron oreprocess.

Such compounds in contact with the gas at the time of contact withcatalytic metallic surfaces, or iron, provide benefits, whether added abinitio or generated in situ, from an added material itself capable ofproviding such compounds.

Having described the invention, what is claimed is:

1. In a process for the production of metallic iron from oxidic ironores wherein iron ore in particulate form is fed into the process andreduced by a stream of carbon monoxide containing gas heated to atemperature ranging from above about 1000 F. to just below the sinteringtemperature of the ore, the improvement comprising heating said reducinggas to said temperature, and adding to said gas an additive selectedfrom the group consisting of sulfur and heat-decomposable sulfurcompounds to cause said additive to be present in the gas during theheating thereof, and while the gas is passing through a temperatureranging from about 800 F. to about 1500 F. to suppress reversion of thecarbon monoxide.

2. The process of claim 1 wherein the additive is provided in the gas ineffective concentration ranging from about 5 to about 1000 parts, permillion parts of gas.

3. In a process for the production of metallic iron from oxidic ironores wherein iron ore in particulate form is fed into the process,staged in a series of beds fluidized by injecting carbonmonoxide-containing gas heated to a .temperature ranging from aboveabout 1000 F. to just below the sintering temperature of the ore, andreduced, at least a portion of the reducing gas is Oxidized, withdrawnfrom the process, cooled and regenerated by removal of oxidizedcomponents, reheated in the presence of catalytic metal surfaces andthence recycled to the -pI'0'CSS,"the improvement comprising heatingsaid reducing gas to said temperature, and adding to said gas anadditive selected from the group consisting of sulfur andheat-decomposable sulfur compounds to cause said additive to be presentin the gas during the heating thereof, while in contact with thecatalytic metal surfaces, and while the gas is passing through atemperature ranging from about 800 F. to about 1500" F. to suppressreversion of the carbon monoxide.

4. In a process for the production of metallic iron wherein oxidic ironore is successively reduced in a plurality of staged fluidized reductionzones with carbon monoxide-containing gases at temperatures above about800 F., whereby said gases are partially oxidized to carbon dioxide andwherein said partially oxidized gases are cooled below about 800 F. andregenerated for further use and then reheated in contact with catalyticmetal surfaces to temperatures above about 800 =F., the improvementcomprising adding to said regenerated gas before reheating an additiveselected from the group consisting of sulfur and heat-decomposablesulfur compounds in an amount sutficient to suppress reversion of thecarbon monoxide.

5. The process of claim 4 wherein the additive is hydrogen sulfide in anamount suflicient to provide a concentration of about 5 to about 1000parts, per million parts of regenerated gas.

6. The process of claim 3 wherein the additive is provided in effectiveconcentration ranging from about 5 to about 1000 parts, per millionparts of gas.

7. The process of claim 3 wherein the additive is a divalent sulfurcompound provided in effective quantities ranging from about 20 to about300 parts, per million parts of gas.

8. The process of claim hydrogen sulfide.

9. The process of claim 3 wherein the additive is provided in elfectiveconcentration ranging from about 50 to about 200 parts, per millionparts of gas.

10. The process of claim 9 wherein the additive is a divalentsulfur-containing compound.

11. In a process for the production of metallic iron by direct reductionof particulate oxidic iron ores wherein ore is successively reduced in aplurality of staged fluidized reduction zones, including ferric andferrous reduction zones, operated at temperatures ranging from about1000 F. to about 1800 F. by preheated carbon monoxide-containing gasinjected into a ferrous reduction zone, the improvement comprisingadding and maintaining from about 5 to about 1000 parts of an additiveselected from the group consisting of sulfur and heatdecomposable sulfurcompounds to the gas, based on a million parts of gas, while preheatingthe gas through a temperature range of from about 800 F. to injectiontemperature, to suppress carbon monoxide reversion.

12. In a process for the production of metallic iron by direct reductionof particulate oxidic iron ores wherein the ore is successively reducedin a plurality of staged fluidized reduction zones including a ferricand a ferrous reduction zone, and wherein hydrocarbon fuel is directlyinjected into a ferrous reduction zone operated at temperatures rangingfrom about 1300" F. to about 1700 F. to generate carbonmonoxide-containing gases which reduces the ferrous oxide to from aboutto about 98 percent metallization, at least a portion of the reducing 3wherein the additive is gas is oxidized, withdrawn from the process,cooled, regenerated by removal of oxidized components, reheated in thepresence of catalytic metal surfaces and thence reinjected into theprocess, the improvement comprising adding to the injected gas fromabout 5 to about 1000 parts of an additive selected from the groupconsisting of sulfur 0r heat-decomposable sulfur compounds, based on amillion parts of generated gas, to suppress carbon monoxide reversion.

13, The process of claim 12 wherein the additive is a divalentsulfur-containing compound.

14. The process of claim 12 wherein the additive is hydrogen sulfide.

15. The process of claim 5 wherein said hydrogen sulfide is provided ina concentration of about 20 to 300 parts per million parts ofregenerated gas.

References Cited UNITED STATES PATENTS 2,711,368 6/1955 Lewis 75-262,740,706 4/1956 Pall et a1 7535 2,835,557 5/1958 West et al 75-263,020,149 2/1962 Old et al 75-26 BENJAMIN HENKIN, Primary Examiner.

